It is well known in many industries to manufacture reinforcing mats for use in adding strength to composite materials. Such mats are, in fact, generally referred to as composite reinforcements. These mats are then impregnated with a liquid material, such as a resin, a bitumen or the like to form a composite material.
Since it is common to prepare the composite reinforcement mats at a place and time remote from the place and time of impregnating it, it is necessary to maintain the fibers of the mats in a predetermined configuration from the point of manufacture until the point of impregnation, at which the fibers are effectively permanently oriented. In fact, it is in some cases necessary to bring more than one mat together at the point of impregnation, orient them relative to each other, and then impregnate them, locking in the relative orientation of the respective mats.
In general, the fibers used to comprise the mats have high melting points or have structural orientations internal to the fibers which could be compromised if the fibers were heated to a high enough temperature to effect any thermal bonding or fusion between the fibers. Likewise, certain adhesives which could be used to secure the fibers in the desired orientation in the mat are undesirable, because their presence adversely affects the ability of the impregnating resin or liquid to fully wet and saturate the mat at the time of impregnation. Even further, the very impregnation process works best when the reinforcing fibers are held together in only proximate relationship, but are not affixed to each other, as this allows the best penetration of the impregnating liquid.
To avoid these problems, the general prior art solution has been to fabricate a mat of the reinforcing fibers by either weaving the fibers together or orienting them into the desired relationship, and then securing them in this configuration, at least temporarily, by stitching or knitting the mat together using a filament. Just as adhesives for securing the fibers must be compatible with the ultimate impregnating agent, the filament used should also be compatible, that is, it should be fully capable of being wetted and saturated by the impregnating agent. For this reason, some filaments which could be thermally fused after stitching or knitting are simply incompatible with the impregnating agent. An example of this would be the incompatibility of a fusible polypropylene filament with a polyester impregnant.
Stitching or knitting inherently provides relatively large loops or other closed circuits of the filament with only a small percentage of the filament sufficiently proximate to other portions of the filament to allow fusion or bonding of the filament portions. When reinforcing mats are stitched or knitted together in the manner known in the prior art, any activity which causes breaks in the filament or pulls the filament out of place can result in catastrophic disruption of the filament matrix which the stitching or knitting has created. For example, cutting the mat, snagging the filament and the like, especially snagging the filament while painting the impregnating liquid into the mat, can all result in “unzipping” the filament, destroying the predetermined fiber orientation.
It is therefore, an unmet need of the industry to provide a reinforcing mat wherein the fibers are held securely in a predetermined orientation relative to each other prior to impregnation by a compatible filament which has been thermally fused to itself at junctures in the filament after the knitting or stitching process.